Several electronic stability control systems currently exist. Example stability control systems are yaw stability control systems (YSC) and roll stability control systems (RSC). The stability control systems are utilized to maintain controlled and stable vehicle operations for improved vehicle and occupant safety. The stability control systems are often used to maintain vehicle tractions and to prevent or mitigate a roll over event.
YSC systems typically compare the desired direction of the vehicle, based upon the steering wheel angle, and the direction of travel. By regulating the amount of braking at each corner of the vehicle, the desired direction of travel may be maintained.
While towing, a vehicle-trailer combination has a physical phenomenon based on the different parameters of the vehicle and trailer such that at a certain speed lateral disturbances to the trailer may cause divergent trailer yaw oscillations. This disturbance may be a road bump, cross-winds, aerodynamic loads caused by a passing vehicle, etc. The trailer yaw oscillations may develop into an unstable situation, which has an associated speed that is described as the critical speed. The oscillations experienced by the trailer are transferred through the trailer hitch to the vehicle. The oscillation motion of the trailer occurs about the vehicle vertical axis, known as the yaw axis.
One technique for minimizing the oscillations, and thus trailer sway is to apply all tow vehicle brakes and reduce engine torque in order to bring the vehicle combination below the critical speed as quickly as possible. Another technique is to actively brake selected wheels of the vehicle to counteract the oscillations and/or to counteract the forces exerted on the vehicle by the trailer. Although the stated techniques provide some desired sway reduction, they are performance limited by the brake actuation capabilities of the tow vehicle. Tow vehicle braking alone causes an increase in trailer hitch force on the tow vehicle, which causes an immediate reduction in vehicle stability. Application of the vehicle brakes at the extreme ends of the trailer sway motion may increase the instability and cause the trailer to sway further into or towards the vehicle. In certain situations such a technique is incapable of adequately minimizing such oscillations and/or minimizing such oscillations in a desired time frame.
Thus, there exists a need for an improved stability control system that provides improved performance and operating efficiency for trailerability of a vehicle.